Granular activated carbons (GAC) are widely used for gas separation and storage. During operation, GAC beds can develop large temperature gradients that reduce the efficiency of the adsorption or storage system in which they are operating. The magnitude of this temperature gradient depends upon the heat of adsorption of the gas being adsorbed or desorbed, the thermal conductivity of the GAC bed, and the heat transfer coefficient of the containment vessel. Typically, the temperature drop in a packed carbon bed during desorption of a gas is several tens of degrees. For example, Barbosa Mota [1] reports that for a natural gas storage vessel discharged from a pressure of 35 atmospheres (atm.) to 1.2 atm., over a period of 1.6 hours, the bed temperature dropped from 20.degree. C. to -19.degree. C., a drop of 39.degree. C. Since the volume of gas desorbed at a given pressure decreases as the GAC temperature decreases, a large amount of gas is retained on the carbon and is thus not available for use. The thermal conductivity of GAC is inherently low because of the disordered structure of the carbon, and its low bulk density (typically 0.4-1.0 g/cm.sup.3). The thermal conductivity of a packed bed of GAC is even lower because of the low pack density of the bed (typically 0.4-0.6 g/cm.sup.3) and the additional particle to particle contact resistance.
Thermal conductivity data for GAC in packed beds are somewhat limited. Gurgel and Grenier [2] report thermal conductivity measurements made using a steady state method on a packed bed of commercial GAC (AC 35 supplied by CECA) in the presence of methanol. The reported packed carbon bed conductivity varied with methanol pressure over the range 0-110 millibar, from 0.14 W/m.cndot.K to 0.17 W/m.cndot.K at a packing density of 0.65 g/cm.sup.3. The derived grain conductivity for the GAC was 0.61-0.65 W/m.cndot.K for methanol adsorbate concentrations from 0 to 0.3 g/g. Measurements on the same GAC by Guilleminot et al [3] yielded a bed thermal conductivity of 0.19 W/m.cndot.K. Critoph and Turner [4] have measured the conductivity of packed carbon beds in the presence of ammonia. The carbon used in their work was a coconut shell GAC (type 208C) supplied by Sutcliffe-Speakman Co. Ltd. The reported bed thermal conductivity was 0.165 W/m.cndot.K in the presence of ammonia, and the grain conductivity varied from 0.85-1.25 W/m.cndot.K as a non-linear function of concentration. Although the bed packed-density was not explicitly reported by Critoph and Turner, it can be estimated to be approximately 0.5 g/cm.sup.3.